Inositol hexaphosphate guanosine diphosphate phosphotransferase from Phaseolus aureus

Inositol hexaphosphate guanosine diphosphate phosphotransferase which transfers phosphate from inositol hexaphosphate to guanosine diphosphate, synthesizing guanosine triphosphate, has been isolated from germinating mung bean. A purification of 86-fold with 33% recovery has been obtained and the protein was made homogeneous after polyacrylamide gel electrophoresis. The MW of this enzyme was ca 92000. The optimal pH was 7·0 and Mn²⁺ was stimulatory. Inositol hexaphosphate was the most active donor of the phosphoryl group (P) to GDP. Inositol penta- or tetra-phosphate (mixed) was partially active, but inositol pentaphosphate produced in this reaction did not act further as phosphate donor. The transfer of P from inositol hexaphosphate was mediated through a phosphoprotein. Polyphosphate (poly Pi), pyrophosphate (PPi) and orthophosphate (Pi) were inactive in this reaction. ADP, CDP and UDP could not substitute for GDP, neither could dGDP nor GMP accept P from inositolphosphate. GTP inhibited the reaction, but ATP did not interfere with the reaction. The products have been shown to be [GMP- ³²P] and inositol pentaphosphate by several criteria. The reaction is practically irreversible. K_m values for GDP and inositol hexaphosphate were 1·1 × 10⁻⁴ M and 1·6 × 10⁻⁶ M respectively.     

Effect of adenine nucleotides and pyrophosphate on the exchange of transferrin-bound carbonate.

1. ATP, ADP and pyrophosphate accelerate the exchange of carbonate of the transferrin-iron-carbonate ternary complex, while AMP, cyclic AMP and phosphate have no effect. 2. ATP promotes carbonate exchange without removing iron from transferrin, whereas pyrophosphate effectiely attacks both the anion and iron components of the ternary complex. 3. Transferrin readily takes over iron from its ATP or pyrophosphate complex. 4. Neither ATP nor pyrophosphate can substitute for carbonate of the ternary complex. These results fit in well with the concept that ATP may play a direct role in the iron uptake by reticulocytes.     

Studies on the mechanism of iron release from transferrin.

Iron release from human, rabbit, rat and sheep transferrin, chicken conalbumin and human lactoferrin was measured by the change in absorbance of solutions of the iron-protein complexes or by the release of 59Fe from the protein conjugated to agarose. Several phosphatic compounds and iron chelators were able to mediate the process (ATP, GTP, 2,3-diphosphoglycerate, inositol hexaphosphate, pyridoxal 5-phosphate, cytidine 5-triphosphate, pyrophosphate, inorganic phosphate, citrate, EDTA, oxalate, nitrilotriacetate). The greatest rate of iron release was found with pyrophosphate and the least with inorganic phosphate. Different rates of iron release were obtained with the different proteins, greatest with human transferrin and least with lactoferrin. With each of the proteins and the mediators there was a linera relationship between the H+ concentration and the rate of iron release. At any given pH the rate of iron release increased to a maximal rate as the mediator concentration was raised. It is concluded that iron release from transferrin under the conditions of these experiments involves an initial interaction between H+ and the iron-transferrin complex followed by release of the iron under the action of the mediator.     

Reaction of DNA-bound Co(II)bleomycin with dioxygen.

The aerobic oxidation of Co(II)bleomycin bound to calf thymus DNA has been investigated in relation to the mechanism of reaction in solution in the absence of DNA. Kinetics of dioxygenation of the Co(II) complex were followed by spectrophotometric and electron spin resonance spectroscopy as well as dioxygen analysis. The reaction is slower than when carried out in solution; its rate is inversely related to the ratio of DNA base pairs to Co(II)bleomycin. The subsequent oxidation reaction, observed spectrophotometrically and by dioxygen analysis, is second order in cobalt complex. The calculated second order rate constant is also inversely related to the base pair to metal complex ratio. Once this ratio exceeds three, the reaction rate slows significantly with each additional increment of DNA added to the starting reaction mixture. Taking advantage of the high stability of O(2)-Co(II)bleomycin bound to greater than a 3-fold excess of DNA base pairs, it could be demonstrated that the rate constant for oxidation of two O(2)-Co(II)bleomycin molecules is much slower than that for O(2)-Co(II)bleomycin plus Co(II)bleomycin. With the same technique it was observed that the metal centers of O(2)-Co(II)bleomycin and Fe(II)bleomycin also undergo oxidation. The binding to DNA of both solution products of the oxidation of Co(II)bleomycin by O2 was examined by 1H NMR spectroscopy. Peroxy-Co(III)bleomycin, Form I, binds with higher affinity than Co(III)bleomycin, Form II. At lower ionic strength, the size of the DNA binding site for each form is about 2 base pairs/molecule of drug.     

Inhibition of photophosphorylation by ATP and the role of magnesium in photophosphorylation.

ATP and pyrophosphate at high concentration (greater than 1 mM) inhibited photophosphorylation of isolated spinach chloroplasts in the normal salt medium and did not cause stimulation of electron transport. The inhibition of photophosphorylation by ATP or pyrophosphate was shown to be abolished by the addition of excess MgCl2, ADP and phosphate. It has been demonstrated that the rates of photophosphorylation in the absence and presence of ATP or pyrophosphate are determined similarly by the concentrations of magnesium-ADP (Mg - ADP-) and magnesiumphosphate (Mg - Pi) complexes. It is highly probable that Mg - ADP- and Mg - Pi, but not free ADP and free phosphate, are the active form of the substrates of photophosphorylation. This is in support of the view that ATP inhibits photophosphorylation by decreasing the concentration of Mg2+ which is available for the formation of the complex with ADP and phosphate.     

Study on the interaction between hemoglobin Izu (Macaca) and organic phosphates by spin labeling

ESR spectra of the carbonmonoxy, oxy, and deoxy derivatives of hemoglobin Izu [Hb Izu (Macaca): beta 83 (EF 7) Gly leads to Cys] labeled at cysteine beta 83 with maleimide spin label have been observed in the presence and absence of 2,3-diphosphoglycerate and inositol hexaphosphate. The tau c values obtained from the spectra indicated that inositol hexaphosphate binds to all the derivatives of Hb Izu, but 2,3-diphosphoglycerate only to the deoxy derivatives.     

Mechanisms of hydrolysis of adenosine 5'-triphosphate, adenosine 5'-diphosphate, and inorganic pyrophosphate in aqueous perchloric acid

The acid-catalyzed hydrolysis of adenosine 5'-triphosphate (ATP) has been found to give rise both to adenosine 5'-diphosphate (ADP) and inorganic phosphate and to adenosine 5'-phosphate (AMP) and inorganic pyrophosphate. Kinetic and isotope studies on the mechanism of hydrolysis of ATP therefore depend on a knowledge of the mechanism of hydrolysis of the polyphosphate products, ADP and inorganic pyrophosphate. The latter reactions have been studied over the acidity range 1--5 M perchloric acid at 25 degrees C while the more complex problem of the hydrolysis of ATP has been followed at a single acidity (3 M perchloric acid). The positions of bond fission have been determined for both ATP and ADP.     

Non-enzymatic ATP-mediated binding of hydroxymethyl derivatives of aromatic hydrocarbons to DNA

ATP mediates covalent binding of hydroxymethyl derivatives of aromatic hydrocarbons to DNA. This non-enzymatic reaction has been studied with 6-[14C]hydroxymethylbenzo[alpha]pyrene (]14C]BP-6-CH2OH) and 7-[14C]-hydroxymethylbenz[alpha]anthracene ([14C]BA-7-CH2OH) at 37 degrees C in Tris buffer (pH 7.0). While ADP mediates the reaction 25-50% as well as ATP, six other possible phosphate donors including AMP were inactive as cofactors. A complex response to ATP occurred in which low binding of BP-6-CH2OH or BA-7-CH2OH was observed at concentrations of ATP below 2.5 mM, but a greater than linear response to higher concentrations of ATP was observed until ATP was saturating. Binding of the substrates to RNA was much lower than to DNA. Fluorescence spectra of BP-6-CH2OH bound to DNA were almost identical to the spectra of 6-bromomethylbenzo[alpha]pyrene bound to DNA and free 6-methylbenzo]alpha]pyrene, indicating that ATP-mediated binding of BP-6-CH2OH to DNA occurs at the 6-methyl group. The fate of ATP and ADP in the binding reaction of BP-6-CH2OH was examined by thin layer chromatography. Loss of one phosphate group occurs during the reaction. With ATP the rate of loss is about 100-fold greater than the rate of binding of BP-6-CH2OH to DNA. This implies that the binding reaction proceeds through formation of a presumed reactive and unstable phosphate ester intermediate which then inefficiently binds to DNA.     

Photophosphorylation sensitized by chlorophyll in the adsorbed state]

Products of phosphate oxidation in a weak alkaline medium in the electrolysis and in the reaction, photosensitized by chlorophyll, are studied. It is shown that besides perphosphates, pyrophosphate can be formed under electrochemical phosphate oxidation. Phosphate was used as an electron donor and the air oxygen was an electron acceptor in the red-ox reaction, photosensitized by chlorophyll. The reaction was accompanied by the decrease of inorganic phosphate content in the reaction medium and by the phosphorylation of ADP to ATP. The mechanism of photophosphorylation is discussed on the basis of the data obtained.     

Rate enhancement of the electron transfer of the adrenodoxin-adrenodoxin reductase system by inorganic and nucleotide phosphates

Phosphate and pyrophosphate increased the rate of reduction of adrenodoxin by NADPH-adrenodoxin reductase and NADPH, pyrophosphate being one order more effective than the former. However, the cytochrome c reduction by the electron transport system was inhibited in the presence of inorganic (pyro)phosphate. On the other hand, ADP and ATP enhanced the rates of reduction of both adrenodoxin and cytochrome c through adrenodoxin by the electron transport system. GTP also enhanced the rate of reduction of cytochrome c by this system, whereas AMP showed no appreciable enhancement. These inorganic and nucleotide phosphates did not affect the rate of ferricyanide reduction by the reductase.     

Inhibition of photophosphorylation by ATP and the role of magnesium in photophosphorylation

ATP and pyrophosphate at high concentration (> 1 mM) inhibited photophosphorylation of isolated spinach chloroplasts in the normal salt medium and did not cause stimulation of electron transport. The inhibition of photophosphorylation by ATP or pyrophosphate was shown to be abolished by the addition of excess MgCl₂, ADP and phosphate. It has been demonstrated that the rates of photophosphorylation in the absence and presence of ATP or pyrophosphate are determined similarly by the concentrations of magnesium-ADP (Mg · ADP^?) and magnesium-phosphate (Mg · P_i) complexes.It is highly probable that Mg · ADP^? and Mg · P_i, but not free ADP and free phosphate, are the active form of the substrates of photophosphorylation. This is in support of the view that ATP inhibits photophosphorylation by decreasing the concentration of Mg²⁺ which is available for the formation of the complex with ADP and phosphate.     

A comparative study of the interactions of bleomycin with nuclei and purified DNA

Fe(III)-bleomycin associates strongly with rat liver nuclei and binds to nuclear DNA. Metal-free and Cu(II)-bleomycin, however, do not bind to nuclei. The treatment of nuclei with activated iron-bleomycin results in nucleic base and base propenal release from the DNA, and also gives membrane peroxidation. Isolation and quantitation of the base propenals and free bases released subsequent to activated bleomycin treatment reveal an alteration in the stoichiometry of these products compared to those released from purified DNA. With nuclei, significantly less propenal is formed, although the yield of free base is equivalent to that from purified DNA. The membrane peroxidation products from nuclei are the same as those obtained from microsomal membranes treated with activated bleomycin. Superoxide dismutase inhibits the membrane peroxidation but has no effect on the DNA breakage reactions. The results implicate a role for iron in mediating the in vivo action of bleomycin and also reveal a potentially toxic effect, membrane peroxidation, separate from DNA damage.     

Iron-bleomycin interactions with oxygen and oxygen analogues. Effects on spectra and drug activity.

Despite extensive structural dissimilarities, iron . bleomycin complexes and heme-containing oxygenases display remarkable similarities in binding oxygen antagonists and in spectral properties deriving from bound iron. Fe(II)-bleomycin reversibly forms a complex with either CO or isocyanide (lambda max = 384 and 497 nm, respectively), either of which interfere with its oxygen-dependent cleavage of DNA. A similar but paramagnetic complex forms with NO (lambda max = 470 nm; AN = 24 G). In contrast, cyanide enhances bleomycin activity against DNA. Complexes of bleomycin and FE(III), formed either by direct association or by autoxidation of the Fe(II) . bleomycin complex, exhibit indistinguishable EPR and visible spectra, which change characteristically with pH. At neutral pH, Fe(III) . bleomycin is a low spin complex (g = 2.45, 2.18, 1.89; lambda max = 365, 384 nm) and, at low pH, it is a high spin rhombic complex (geff = 9.4, 4.3; lambda max = 430 nm). These complexes are interconvertible (pK 4.3). Fe(II) . bleomycin oxidation, although reversible by spectral criteria, is accompanied by drug inactivation unless DNA is present.     

Preparation of adenosine nucleotide derivatives suitable for affinity chromatography

Methods of synthesizing a series of chemically-defined AMP, ADP, ATP, adenylyl imidodiphosphate and pyrophosphate derivatives suitable for affinity chromatography are extensively described. Each derivative has a single primary amino group at the end of a hexamethylene ;spacer' chain for attachment to CNBr-activated agarose. The synthesis of the derivative where the ;spacer' arm is attached directly to the 8 position of the adenine ring to produce 8-(6-aminohexyl)amino-AMP involves the direct bromination of AMP in the 8 position followed by displacement of the halogen by 1,6-diaminohexane. This monophosphate derivative can then be converted into the corresponding di- or triphosphate forms by direct phosphate condensation with carbonyl di-imidazole. A second series of adenosine phosphate derivatives with the phosphate moieties unsubstituted has been similarly prepared from N(6)-(6-aminohexyl)-AMP (Guilford et al., 1972). A third type of ligand has been synthesized by condensing the phosphoryl imidazolide of AMP with 6-aminohex-1-yl phosphate. This compound, P(1)-(6-aminohex-1-yl) P(2)-(5'-adenosyl) pyrophosphate, has an unsubstituted adenine ring. The synthesis of a fourth type of ligand, 6-aminohex-1-yl pyrophosphate, was done by heating 6-aminohexan-1-ol with crystalline pyrophosphoric acid under reduced pressure. The structures of the synthesized compounds were confirmed by chemical, electrophoretic and chromatographic methods and by u.v. spectrometry. The general applicability of the synthetic methods used is discussed in relation to the preparation of other affinity adsorbents. Examples are given where these derivatives have been successful in reversibly binding dehydrogenases, kinases and myosin and its proteolytic subfragments. The partial purification of rat liver glucokinase on an ADP derivative is shown.     

Acceleration of tetramer formation by the binding of inositol hexaphosphate to hemoglobin dimers.

The aggregation of deoxyhemoglobin dimers was studied by dropping the pH of a dilute solution of deoxyhemoglobin originally at high pH. In the presence of inositol hexaphosphate, a sharp increase in the rate of dimer association was observed. At higher concentrations of the phosphate, the rate decreased to a value close to that seen in the absence of phosphate. These observations require that inositol hexaphosphate binds to deoxyhemoglobin dimers. The dependence of the aggregation rate on phosphate concentration occurs because the reaction of a dimer containing bound phosphate with a phosphate-free dimer is 30 to 50 times faster than either the association of phosphate-free dimers or the association of dimers both containing bound phosphate.     

Activated bleomycin. A transient complex of drug, iron, and oxygen that degrades DNA

"Activated bleomycin" is an oxygenated iron drug complex which embodies the drug's DNA-cleaving activity. This activity is exercised on DNA, if present, but if DNA is absent, the drug itself is inactivated. Hyperfine interactions in the EPR spectra of activated bleomycin prepared with 57Fe(II) and 17O2 demonstrate the presence of iron as Fe(III) and of bound oxygen originating in dioxygen. Bleomycin can also be activated with Fe(III) and either H2O2 or ethyl hydroperoxide. These latter reactions do not produce a ferrous intermediate nor do they require O2. But O2 is required for the reaction of activated bleomycin with DNA to yield the malondialdehyde-like chromogens used to monitor DNA degradation. The attack on DNA is quantitatively concurrent with the decay of activated bleomycin, however generated.     

Inhibition of NADH-methemoglobin reductase by organic phosphates.

The organic phosphate allosteric effectors of hemoglobin, inositol hexaphosphate, 2,3-diphosphoglycerate, and ATP, interact with NADH-methemoglobin reductase (NADH-diaphorase). Significant inhibitory effects on the enzyme were found when dichlorophenolindophenol, or ferricyanide were used as electron acceptors in place of methemoglobin. In contrast, apparent stimulation of enzyme activity was observed when adult human methemoglobin was used as the electroganic phosphate on the rate of reaction due to its interaction with the substrate methemoglobin to produce the favored T type of quaternary conformation. The inhibitory effect of inositol hexaphosphate on the enzyme is associated with a perturbation in the reactivity of essential sulfhydryl group(s) on the enzyme. It is suggested that the interaction of the organic phosphate with the enzyme as well as with the substrate is significant in determining the overall rate of methemoglobin reduction.     

Formation of ribonucleotide 2'',3''-cyclic carbonates during conversion of ribonucleoside 5''-phosphates to diphosphates and triphosphates by the phosphorimidazolidate procedure.

Ribo- and 2'-deoxyribonucleoside 5'-di- or triphosphates are commonly synthesized by reaction of inorganic phosphate or pyrophosphate with phosphorimidazolidates obtained by reaction of nucleoside 5'-phosphates with 1,1'-carbonyldiimidazole. The latter reaction, however, converted UMP, CMP, IMP, GMP, and AMP in high yield to the 2',3'-cyclic carbonate derivatives of their phosphorimidazolidates. Acidic treatment of the product from AMP gave AMP 2',3'-cyclic carbonate dihydrate; this was characterized by its uv, ir, and pmr spectra and by its conversion to adenosine 2',3'-cyclic carbonate by acid phosphatase and to AMP by basic hydrolysis. ADP or ATP synthesized by the phosphorimidazolidate method contained equal or greater amounts of their respective 2',3'-cyclic carbonates. The latter could be quantitatively converted to ADP and ATP, respectively, by 4-hr hydrolysis at pH 10.5, 22 degrees. ADP or ATP can be synthesized without concomitant 2',3'-cyclic carbonate formation by reaction of AMP with phosphorimidazolidates of inorganic phosphate or pyrophosphate.     

Escherichia coli dnaB protein. Affinity chromatography on immobilized nucleotides.

The purification of the Escherichia coli dnaB protein by affinity chromatography on nucleotides bound to agarose is described. The dnaB protein, which contains an associated ribonucleoside triphosphatase activity (Wickner, S., Wright, M., and Hurwitz, J. (1974) Proc. Natl. Acad. Sci. U. S. A. 71, 783-787) binds to immobilized ATP, ADP, and UDP, but not to AMP. The type of linkage of ATP to agarose influences the adsorption, elution, and purification of the enzyme. Optimal purification is achieved using ATP bound to agarose via its oxidized ribose moiety. By this means, the dnaB protein can be obtained at least 95% electrophoretically pure after only three purification steps. The enzyme can be eluted from immobilized nucleoside-5'-di- and -triphosphates by ATP, ADP, and pyrophosphate, but not by AMP or orthophosphate. ADP and pyrophosphate, as well as the substrate ATP in high concentration are at the same time inhibitors of the ribonucleoside triphosphatase. The dnaB complementing and ribonucleoside triphosphatase activities could not be separated from each other by affinity chromatography, supporting the finding of others that they both reside on the same protein complex, namely a dnaB multimer. The results indicate that the dnaB protein binds to immobilized nucleotides by means of its ribonucleoside triphosphatase, and that at least the pyrophosphate moiety is essential for adsorption as well as elution of the enzyme.